Amplifying system



1A VENTOR George L. Beers B J ATTORNEY,

Oct. 18, 1932. G. BEERS AMPLIFYING SYSTEM Flled Aprll 25 1951 PatentedOct. 18, 1932 UNITED STATES PATENT OFFICE GEORGE LISLE BEEBS, OICOLLINGSWOOD, NEW JERSEY, ABSI GNOB, 3'! ml! ASSIGN- MENTB, TO RADIOCORPORATION 01' AMERICA, 01' NEW YORK, N. Y .A CORPORATION 01! DELAWAREAMPLII'IING SYSTEM Application filed April 25, 1881. Serial Io. 582,753.

My invention relates to amplifying systems and, more particularly, tosystems of the type wherein piezo-electric crystals are employed ascoupling devices.

It is a well-known fact that sections cut from piezo-electrically activematerials, such as tourmaline, or quartz, may be utilized for thepurpose of selectively coupling one electric circuit to another. When soused, a crystal section, theoretically, should offer re atively highimpedance to all frequencies other than its natural frequency ofvibration.

In actual practice, however, it has been found that the selectivity of acrystal section departs considerably from the selectivity theoreticallyattainable. The reason for this is found in the fact that theinter-electrode capacity of the crystal holder offers a path between thecoupled circuits, the reactance of which is substantially independent ofthe crystal section.

It is, of course, possible to neutralize the effect of theinter-electrode capacity by a bridge circuit similar to the circuitsused for neutralizing the grid-plate capacity in thermionic tubes. Suchcircuits, nevertheless, require critical adjustment for best results andtheir inclusion in factory-made radio receivers requires skilledoperatives.

It is, accordingly, an object of my invention to provide an amplifylngsystem wherein the full selectivity of a piezo-electric crystal may beutilized.

Another object of my invention is to provide a piezo-electric crystalholder wherein the inter-electrode capacity is compensated.

Another, and more specific, object of my invention is to providenon-critical means for compensating the inter-electrode capacity of apiezo-electric crystal holder.

The foregoing objects, in a preferred embodiment of my invention, areattained by so re-locating the electrodes, between which the detrimentalcapacity exists, with respect to the crystal section, that a groundedelectrostatic shield may be interposed between them.

The novel features that I consider characteristic of my invention areset forth with particularity in the appended claims. The invention inits entirety, together with additional objects and advantages thereof,will best be understood from the following descri tion of a specificembodiment, when rea in connection with the accompanying drawing.

The single figure of the drawing is a view, partly perspective andpartly diagrammatic, of a portion of an amplifying system includpig apreferred embodiment of my invenion.

The apparatus illustrated in the drawing includes a thermionic tube 1,hereinafter referred to as a source of alternating potential, and asecond thermionic tube 3, hereinafter referred to as the amplifier.Although thermionic tubes of the three-electrode type are illustrated asthe source and amplifier, respectively, my invention 'is not restrictedthereto, it being, of course, applicable to amplifying systems of anydesired type.

The output electrode 5 of the source and the input electrode 7 or gridof the amplifier are coupled through a piezo-electric crystal 9, thedimensions of which are such as to render it resonant to the frequencyof the potentials delivered by the said source. The piezo-electriccrystal is supported between a pair of flat upper electrodes 11 and 13that are, respectively, connected to the aforementioned output and inputelectrodes of the thermionic devices and a third electrode 15, which isso disposed with respect to the said two fiat electrodes as to define acrystal receiving space. Preferably, the first mentioned pair ofelectrodes and the third elec trode are mounted upon and carried by ablock 17 of insulating material such as porcelain or the like.

A metallic shielding element 19 is vertically supported from the thirdor lower electrode and is disposed between the free ends of the upperelectrodes. The shielding device, preferably, is provided with acut-away portion 21 so dimensioned as to accommodate the crystal. Aground connection 23 for the shielding device and the lower electrode isprovided and ground connections 25 and 27 are also provided for thesource and the amplifier.

In the operation of the system as disclosed,

alternating potentials appearing across the output circuit of the sourceare impressed between the electrode 11, connected to the plate thereof,and the lower electrode 15 upon which the crystal section rests. Suchpotentials, if at the frequency to which the crystal section isresonant, cause the said section to vibrate in unison therewith and, byreason of the fact that the crystal, when vibrating, develops potentialsacross its faces, an electric field appears between the flat electrode13 connected to the grid of the amplifier and the common lower electrode15 which is connected to the cathode thereof through ground.

By reason of the fact that the shielding element, which is at groundpotential, is interposed between the input and output electrodes 11 and13 of the crystal holder, it serves to effectively intercept allelectric field lines which originate either at the input or the outputelectrode and thus prevents any transfer of energy between the saidelectrodes by reason of the capacity existing therebetween. In otherwords, the only energy which can pass from the source to the amplifiermust go by way of the crystal element itself and such energy,accordingly, is restricted to the frequency of the crystal and tofrequencies differing therefrom by not more than a few hundred cycles.

My invention, therefore, provides a new and improved coupling devicewhich is vastly more selective than coupling devices known to the priorart. It does not require critical adjustment nor is the adjustmentthereof prone to change during use.

Although I have illustrated and described a specific embodiment of myinvention, numerous modifications thereof will be apparent to thoseskilled in the art to which it pertains. My invention, therefore, is notto be limited except insofar as is necessitated by the prior art and bythe spirit of the appended claims.

I claim as my invention:

1. In combination, means for producing fluctuating potential, amplifyingmeans, coupling means for impressing potentials from said source on saidamplifying means, the coupling means including a piezo-electrio crystaland a plurality of electrodes disposed adjacent thereto, and screeningmeans interposed between certain of said electrodes for minimizing thecapacitive transfer of energy therebetween.

2. The combination set forth in claim 1 characterized in that certain ofthe electrodes, between which the capacity is minimized, are disposedadjacent to the same face of the crystal.

3. The combination set forth in claim 1 wherein certain of theelectrodes, between which the capacity is minimized, are disposedadjacent to the same face of the crystal, and further characterized inthat another of the electrodes is disposed adjacent the opposite face ofthe crystal.

4;. The combination set forth in claim 1 characterized in that thecapacity minimizing means is constituted by an electrostatic shield.

5. The combination set forth in claim 1 wherein the capacity minimizingmeans is constituted by an electrostatic shield and furthercharacterized in that the said shield is connected to a point thepotential of which, in the operation of the system, is lower than thatof the electrodes between which the said means is interposed.

6. The combination set forth in claim 1 wherein the capacity minimizingmeans is constituted by an electrostatic shield 'andfurthercharacterized in that at least one of the plurality of electrodesis electrically connected to the said shield.

7. In an amplifying system, a piezo-electric crystal holder including aplurality of electrodes that define a crystal-receiving space andscreening means interposed adjacent said space for minimizing thecapacitive transfer of energy between certain of said electrodes.

8. A piezo-electric crystal holder including an input electrode and anoutput electrode so disposed with respect to a common electrode as todefine a crystal-receiving space and screening means for preventing thecapacitive transfer of energy between said input and output electrodes.

9. A piezo-electric crystal holder including an input electrode, anoutput electrode and screening means interposed therebetween.

10. A piezo-electric crystal holder including a pair of electrodes, athird electrode disposed in capacitive relation to said pair ofelectrodes, and metallic screening means disposed between the electrodesof said pair, said means being electrically connected to the thirdelectrode.

In testimony whereof, I have hereunto subscribed my name this 20th dayof April,

GEORGE LI SLE BEERS.

